Hi Robin, We are mostly using Oracle 11.2.0.3 and 12.1.0.2. Some of our servers are in the AWS cloud and I can change OS parameters there. But for the servers that are running out of our server room, I need to justify any OS changes that I want. By default the servers allocate half the total memory to shared memory whether or not we are using AMM, or shared memory. Hence, I am trying to figure out what benefits we would get from shrinking /dev/shm on servers where we aren't using shared memory. Would it even make a difference.
---------- Post updated at 10:40 AM ---------- Previous update was at 10:11 AM ----------
For example, I increased the AMM memory on two databases on this server
from 1GB to 3GB, and the total memory allocated when down.
It just seems like Redhat is holding onto shared memory that would be better
off not being shred memory, thus reducing the amount of swap being used.
There are 12 databases on this server, most do not use shared memory.
Code:
BEFORE INCREASE
$: ~ > free -m
total used free shared buffers cached
Mem: 32186 31987 198 0 872 26785
-/+ buffers/cache: 4329 27856
Swap: 20474 4340 16133
$: ~ > df -h /dev/shm
Filesystem Size Used Avail Use% Mounted on
tmpfs 26G 5.4G 20G 22% /dev/shm
AFTER INCREASE
$: ~/scripts/sql > free -m
total used free shared buffers cached
Mem: 32186 29764 2421 0 1038 24912
-/+ buffers/cache: 3813 28372
Swap: 20474 4254 16220
$: ~/scripts/sql > df -h /dev/shm
Filesystem Size Used Avail Use% Mounted on
tmpfs 26G 8.1G 18G 32% /dev/shm
I am running HP-UX B.11.11.
I'm increasing a parameter for a database engine so that it uses more memory to buffer the disk drive (to speed up performance). I have over 5GB of memory not being used.
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Discussion started by: Abhi04
2 Replies
LEARN ABOUT PHP
shmop_open
SHMOP_OPEN(3) 1 SHMOP_OPEN(3)shmop_open - Create or open shared memory blockSYNOPSIS
int shmop_open (int $key, string $flags, int $mode, int $size)
DESCRIPTION shmop_open(3) can create or open a shared memory block.
PARAMETERS
o $key
- System's id for the shared memory block. Can be passed as a decimal or hex.
o $flags
- The flags that you can use:
o "a" for access (sets SHM_RDONLY for shmat) use this flag when you need to open an existing shared memory segment for read
only
o "c" for create (sets IPC_CREATE) use this flag when you need to create a new shared memory segment or if a segment with the
same key exists, try to open it for read and write
o "w" for read & write access use this flag when you need to read and write to a shared memory segment, use this flag in most
cases.
o "n" create a new memory segment (sets IPC_CREATE|IPC_EXCL) use this flag when you want to create a new shared memory seg-
ment but if one already exists with the same flag, fail. This is useful for security purposes, using this you can prevent
race condition exploits.
o $mode
- The permissions that you wish to assign to your memory segment, those are the same as permission for a file. Permissions need to
be passed in octal form, like for example 0644
o $size
- The size of the shared memory block you wish to create in bytes
Note
Note: the 3rd and 4th should be entered as 0 if you are opening an existing memory segment.
RETURN VALUES
On success shmop_open(3) will return an id that you can use to access the shared memory segment you've created. FALSE is returned on
failure.
EXAMPLES
Example #1
Create a new shared memory block
<?php
$shm_key = ftok(__FILE__, 't');
$shm_id = shmop_open($shm_key, "c", 0644, 100);
?>
This example opened a shared memory block with a system id returned by ftok(3).
SEE ALSO shmop_close(3), shmop_delete(3).
PHP Documentation Group SHMOP_OPEN(3)